Thousands of people  rallied in Tehran  on Sunday just before U.S. sanctions against Iran were set to snap back into place.

They were there to mark the 39th anniversary of the U.S. Embassy takeover.

Demonstrators were chanting "down with U.S.A." and "death to Israel." Media outlets report similar rallies were held in other Iranian towns and cities.  Here's a bit of history: In 1979, just months after the Islamic Revolution, insurgents  stormed the U.S. Embassy  in Tehran and held 52 Americans hostage there for 444 days.

The U.S. cut off diplomatic ties with Iran after the hostage crisis.

It's seen as the start of major hostilities between the U.S., its allies and Iran.  An Al Jazeera reporter in Tehran described Sunday's rallies as "bigger" and "angrier" than previous years, mainly because the anniversary coincides with the reinstatement of U.S. sanctions on Iran starting Nov.

5.

Those sanctions  will affect  Iran's energy, shipbuilding, shipping and banking sectors.  Additional reporting from  Newsy affiliate CNN .